Polymer Composition for Microelectronic Assembly

ABSTRACT

Embodiments in accordance with the present invention encompass polymer compositions that are useful in the assembly of microelectronic components onto a variety of substrate materials. Such polymer compositions providing for both holding the microelectronic components at desired positions on a substrate, providing fluxing for the solder bonding of such components to the substrate and remaining in place as an underfill for such components.

TECHNICAL FIELD

Embodiments in accordance with the present invention relate generally topolymer compositions that are useful for mounting microelectroniccomponents to a substrate and more specifically to a polymer compositionthat provides for both holding microelectronic components at desiredpositions on a substrate, providing fluxing for the solder bonding ofsuch components to the substrate and remaining in place as an underfill.

BACKGROUND

While assembled electronic circuitry has been dramatically reduced insize, the use of soldering as a method for forming both an electricaland fixable attachment of electronic components to a substrate hasremained quite prevalent. However, such attachments require that thevariety of components be held in desired positions prior to completingthe aforementioned solder attachments, and post electrical underfillconnection. An underfill connection can increase the thermal fatiguelife of a solder ball connection, environmentally protect theconnection, and provide greater mechanical shock and robustness to theassembled electronic circuitry.

A number of solutions for temporarily holding components in such desiredpositions have been developed and used with some success. For example, atack agent can be used to secure such components to the substrate whilesolder bond or solder ball connections are made through the applicationof heat. After such temporary connections are made, the tack agent canremain as a contaminant or the assembly subjected to an extra processingstep designed to remove such contamination. For some of theaforementioned solutions, a fluxing agent is provided separately fromthe tack agent, for example by applying such fluxing agent in a distinctapplication step, separate from the application of the tack agent. Inother solutions the fluxing agent is provided in a combination with thetack agent, for example where a solder paste is used as the tack agentand fluxing agent is either added thereto or prereacted therewith.

In still other solutions, (see, U.S. Pat. No. 5,177,134 or US PublishedApplication No. 2009/0294515, the '134 patent and the '515 application,respectively) a tack agent and fluxing agent are admixed where uponsoldering, the tack agent either volatilizes or decomposes. However ithas been found that where the tack agent is either volatized ordecomposed at or above solder reflow temperatures, as each of the aboveteaches, either solder reflow is limited, significant contamination fromthe tack agent can remain or specialized process equipment is required.

Therefore new solutions that can provide a single material that holdscomponents in desired positions prior to completing solder attachments(i.e., performs as a tack agent), provide for any fluxing that might bedesired (i.e., performs as a fluxing agent) and also provides a postelectrical connection underfill would be desirable. Further it would beadvantageous if such solutions would eliminate the need for specializedequipment, as described above, and reduce or eliminate the problems withachieving desirable solder reflow and/or associated with anycontamination that might result therefrom.

DETAILED DESCRIPTION

Exemplary embodiments in accordance with the present invention will bedescribed with reference to the Examples and Claims providedhereinafter. Various modifications, adaptations or variations of suchexemplary embodiments described herein may become apparent to thoseskilled in the art as such are disclosed. It will be understood that allsuch modifications, adaptations or variations that rely upon theteachings of the present invention, and through which these teachingshave advanced the art, are considered to be within the scope and spiritof the present invention.

As used herein, the articles “a,” “an,” and “the” include pluralreferents unless otherwise expressly and unequivocally limited to onereferent.

As used herein, the terms “group” or “groups” when used in relation to achemical compound and/or representative chemical structure/formula, meanan arrangement of one or more atoms.

As used herein, molecular weight values of polymers, such as weightaverage molecular weights (M_(w)) and number average molecular weights(M_(n)) are determined by gel permeation chromatography usingpolystyrene standards.

As used herein, polydispersity index (PDI) values represent a ratio ofthe weight average molecular weight (M_(W)) to the number averagemolecular weight (M_(n)) of the polymer (i.e., M_(w)/M_(n)).

As used herein, and unless otherwise stated, polymer glass transitiontemperature (T_(g)) values are determined by differential scanningcalorimetry in accordance with American Society for Testing andMaterials (ASTM) method number D3418.

As used herein, and unless otherwise stated, the polymer decompositiontemperature (T_(d)) is the temperature, determined by thermogravimetricanalysis at a heating rate of 10° C./minute, where a specific weightpercent (wt %) of a polymer has determined to have decomposed. The termsT_(d5), T_(d50) and T_(d95) indicate the temperatures at which 5 wt %,50 wt % and 95 wt % has decomposed.

Unless otherwise indicated, all ranges or ratios disclosed herein are tobe understood to encompass any and all subranges or subratios subsumedtherein. For example, a stated range or ratio of “1 to 10” should beconsidered to include any and all subranges between (and inclusive of)the minimum value of 1 and the maximum value of 10; that is, allsubranges or subratios beginning with a minimum value of 1 or more andending with a maximum value of 10 or less, such as but not limited to, 1to 6.1, 3.5 to 7.8, and 5.5 to 10.

In the operating examples, and unless otherwise indicated, all numbersused in the specification and claims expressing quantities ofingredients, reaction conditions, and so forth are to be understood asbeing modified in all instances by the term “about” to take into accountthe uncertainties associated with determining such values.

Polymers such as poly(propylene carbonates) are well known, and both thepreviously mentioned '134 patent and '515 application teach that suchpolymers are effective tack agents. However, such poly(propylenecarbonates) are also known to be subject to thermal decomposition attemperatures in the range of 200° C. to 280° C., and thus can beproblematic where a material capable of being a tack agent, a fluxingagent and providing underfill is desired. This being especially truewhere a lead-free solder material is to be employed for making thesolder interconnections since such lead-free solders generally have amelting range 30 to 40° C. higher than commonly used lead-containingsolders. For example, the commonly used Sn60Pb40 solder alloy has amelting range from 183 to 190° C. while Sn99.3Cu0.7, used in theexamples provided hereinbelow, melts at 227° C.

Some polymer embodiments in accordance with the present inventionencompass polymers formed from stereospecific norbornane diol and/ordimethanol monomers while other polymer embodiments encompass polymersderived from appropriate alkylene carbonate monomers and theaforementioned norbornane diol and/or dimethanol monomers.Advantageously, some such polymer embodiments have a T_(d50) greaterthan 280° C. while other such polymer embodiments have a T_(d50) greaterthan 310° C. and still other such polymer embodiments have a T_(d50)greater than 340° C. In addition, some such norbornane diol and/ordimethanol containing polymer embodiments have molecular weights (M_(w))in the range of from 5,000 to 300,000, other such embodiments have aM_(w) range of from 25,000 to 200,000 and still other such embodimentsfrom 40,000 to 185,000.

Some of the aforementioned stereospecific norbornane diol and/ordimethanol monomers are represented by and selected from the followingFormulae A, B or C:

Where for each of Formulae A, B and C, n is independently 0, 1 or 2,each of R¹, R², R³ and R⁴ is independently selected from hydrogen or ahydrocarbyl group containing, without limitation, from 1 to 25 carbonatoms, each of R⁵ and R⁶ are independently selected from —(CH₂)_(p)—OH,where p is 0, 1, 2 or 3, and each of X and X′ is independently selectedfrom —CH₂—, —CH₂—CH₂— and —O—, where each X′ is, if present, orientedthe same or opposite the orientation of X. For some embodiments inaccordance with the present invention, p is 1, 2 or 3 for at least oneof R⁵ and R⁶.

As used herein the term “hydrocarbyl” and similar terms, such as“hydrocarbyl group” means a radical of a group that contains carbon andoptionally hydrogen, non-limiting examples being alkyl, cycloalkyl,polycycloalkyl, aryl, aralkyl, alkaryl, alkenyl, cycloalkenyl,polycycloalkenyl, alkynyl, cycloalkynyl and polycycloalkynyl. The term“halohydrocarbyl” as used herein means a hydrocarbyl group where atleast one hydrogen covalently bonded to a carbon has been replaced by ahalogen. The term “perhalocarbyl” as used herein means a hydrocarbylgroup where all such hydrogens have been replaced by a halogen. Inaddition, the term “heterohydrocarbyl” as used herein means ahydrocarbyl group where at least one carbon atom has been replaced witha hetero atom such as oxygen, nitrogen and/or sulfur.

As used herein, the term “alkyl” means a linear or branched acyclic orcyclic, saturated hydrocarbon group having a carbon chain length of fromC₁ to C₂₅. Nonlimiting examples of suitable alkyl groups include methyl,ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl,nonadecyl, isocanyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,cycloheptyl and cyclooctyl. As used herein, the term “heterocycloalkyl”means a cycloalkyl group in which one or more carbons of the cyclic ringhas been replaced with a hetero atom, such as oxygen, nitrogen and/orsulfur. Representative heterocycloalkyl groups include but are notlimited to tetrahydrofuranyl, tetrahydropyranyl, morpholinyl, andpiperidinyl.

As used herein, the term “aryl” means aromatic groups that include,without limitation, phenyl, biphenyl, benzyl, xylyl, naphthalenyl,anthracenyl. As used herein, the term “heteroaryl” means an aryl groupin which one or more carbons of the aromatic ring or rings has beenreplaced with a hetero atom, such as oxygen, nitrogen and/or sulfur.Representative heteroaryl groups include but are not limited to furanyl,pyranyl and pyridinyl.

The terms “alkaryl” and “aralkyl” are used herein interchangeably andmean a linear or branched acyclic alkyl group substituted with at leastone aryl group, for example, phenyl, and having an alkyl carbon chainlength of C₁ to C₂₅. It will further be understood that the aboveacyclic alkyl group can be a haloalkyl or perhaloalkyl group.

As used herein, the term “alkenyl” means a linear or branched acyclic orcyclic hydrocarbon group having one or more double bonds and having analkenyl carbon chain length of C₂ to C₂₅. Non-limiting examples ofalkenyl groups include, among others, vinyl, allyl, propenyl, butenyl,pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl,dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl,heptadecenyl, octadecenyl, nonadecenyl, and isocenyl.

As used herein, the term “alkynyl” means a linear or branched acyclic orcyclic hydrocarbon group having one or more carbon-carbon triple bondsand having an alkynyl carbon chain length of C₂ to C₂₅. Representativealkynyl groups, include but are not limited to, ethynyl, 1-propynyl,2-propynyl, 1-butynyl, 2-butynyl, pentynyl, heptynyl, octynyl, nonynyl,decynyl, undecynyl, dodecynyl, tridecynyl, tetradecynyl, pentadecynyl,hexadecynyl, heptadecynyl, octadecynyl, nonadecynyl, isocynyl.

As used herein, recitations of “linear or branched” groups, such aslinear or branched alkyl, will be understood to include a methylenegroup, groups that are linear, such as linear C₂-C₂₅ alkyl groups, andgroups that are appropriately branched, such as branched C₃-C₂₅ alkylgroups.

For Formulae A, B and C, each X group is depicted as extending upwardout of the page. With Formula A, R⁵ and R⁶ are each depicted asextending upward out of the page, and as such are cis- to one anotherand are exo- relative to the X group. Formula A, therefore is referredto as a polycyclic cis-exo 2,3-diol monomer. With Formula B, R⁵ and R⁶are each depicted as extending downward into the page, and as such arecis- to one another and are endo- relative to the X group. Formula B,therefore, is referred to as a polycyclic cis-endo 2,3-diol monomer.With Formula C, R⁵ is depicted as extending upward out of the page, exo-relative to the X group, R⁶ is depicted as extending downward into thepage, endo- relative to the X group, and trans- relative to one another.Formula C, therefore, is referred to as a polycyclic endo/exo 2,3-diolmonomer or a polycyclic trans 2,3-diol monomer.

For further embodiments of the present invention, for each of FormulaeA, B and C: n is 0; three of R¹-R⁴, are each hydrogen; and one of R¹-R⁴is independently selected from alkyl, cycloalkyl, heteroalkyl,heterocycloalkyl, aryl, heteroaryl and aralkyl, and is oriented exorelative to X. For purposes of illustration, with n=0, X being —CH₂—,R¹, R² and R³ each being hydrogen, R⁴ being a non-hydrogen exo grouprelative to X, and R⁵ and R⁶ each being —CH₂OH, Formulae A, B and C canbe represented by the following Formulae A1, B1 and C1.

For each of Formulae A1, B1 and C1, R⁴ can in each case be independentlyselected from a hydrocarbyl group including, but not limited to thoseclasses and examples as described previously herein, for example, withregard to R¹-R⁴.

Other useful diol monomers, include polycyclic diol monomers representedby the following Formulae D, E and F.

Independently for each further polycyclic diol monomer represented byFormulae D, E and F: m is 0, 1 or 2; Z and Z′ are each independentlyselected from —CH₂—, —CH₂—CH₂— and —O—; Z* is —CH—; R⁷, R⁸, R⁹ and R¹⁰are in each case independently selected from hydrogen, and a hydrocarbylgroup; R¹¹ and R¹² are in each case independently selected from—(CH₂)_(p)—OH, where p for R¹¹ and R¹² is in each case independentlyselected from 0, 1, 2 or 3; and each Z′ is, if present, oriented thesame or opposite the orientation of Z or Z*, respectively.

With Formulae D, E and F, each Z group and Z* group is depicted asextending upward out of the page. With Formula D, each Z′, if present,has an orientation, independently for each m, that is the same oropposite relative to the orientation of Z. With Formulae E and F, eachZ′, if present, has an orientation, independently for each m, that isthe same or opposite relative to the orientation of Z*.

The hydrocarbyl groups from which R⁷-R¹⁰ can each be independentlyselected include, but are not limited to, those classes and examplesrecited previously herein. For each of Formulae D-F, in embodiments ofthe present invention, at least one of R⁷-R¹⁰ is a group independentlyselected from alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl,heteroaryl and aralkyl, and the other R⁷-R¹⁰ group(s), if any, that arenot selected from such non-hydrogen groups, are each hydrogen. Examplesof alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, heteroaryland aralkyl groups from which each of R⁷-R¹⁰ can be selected include,but are not limited to, those classes and examples as recited previouslyherein with regard to R¹-R⁴.

In further embodiments, for each of Formulae D-F: m is 0; three ofR⁷-R¹⁰ are each hydrogen; and one of R⁷-R¹⁰ is independently selectedfrom alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, heteroaryland aralkyl, and is oriented exo relative to Z or Z*. For purposes ofillustration, with m=0, Z being —CH₂—, R⁷, R⁸ and R⁹ each beinghydrogen, R¹⁰ being a non-hydrogen exo group, R¹¹ and R¹² each being—CH₂OH for Formula D and —OH for Formulae E and F, Formulae D-F can berepresented by the following Formulae D1, E1 and F1. For purposes offurther illustration, with m=0, Z being —CH₂—, R⁸, R⁹ and R¹⁰ each beinghydrogen, R⁷ being a non-hydrogen exo group, R¹¹ and R¹² each being—CH₂OH for Formula D and —OH for Formulae E and F, Formulae D-F can berepresented by the following Formulae D1′, E1′ and F1′. It will beunderstood, that unless specifically stated, all Formulae presentedherein are inclusive of the enantiomeric, and diasteriomeric analogsthereof.

Still other diol monomers, include polycyclic diol monomers representedby the following Formula G.

With the polycyclic diol represented by Formula G, Z, R¹¹ and R¹² areeach as described previously herein with regard to Formulae E-F.

Additional diol monomers, include cyclic diol monomers represented bythe following Formulae I through XII.

With Formulae X and XI, R¹³ is independently selected from C₁-C₆ alkyl,such as but not limited to C₁-C₆ linear alkyl or C₃-C₆ branched alkyl.

Further optional polyol monomers include, but are not limited to,hydrocarbyls having two or more hydroxyl groups, such as but not limitedto 2, 3 or 4 hydroxyl groups. Examples of optional diol monomersinclude, but are not limited to: C₁-C₂₅ linear or branched alkylenediols, such as, 1,2-ethylenediol, 1,3-propylenediol and1,2-propylenediol; and polyalkyleneglycols, such as di-, tri-, tetra-and higher ethyleneglycols, di-, tri, tetra- and higherpropyleneglycols. Optional polyol monomers having more than two hydroxylgroups are typically present in small amounts, such as but not limitedto less than 10 mole percent, or less than 5 mole percent, based on thetotal mole percent of hydroxyl functional monomers. Examples of polyolmonomers having more than two hydroxyl groups include, but are notlimited to, trimethylolpropane, pentaerythritol anddi-trimethylolpropane. For some embodiments, the polycarbonate polymeris not derived from polyol monomers having more than two hydroxylgroups.

The polycyclic 2,3-diol monomers represented by Formulae A, B and C canbe prepared by art-recognized methods such as are shown in SyntheticSchemes 1 through 6, shown hereinbelow.

For purposes of non-limiting illustration, the polycyclic cis-exo2,3-diol monomer represented by Formula A can be prepared in accordancewith the following Synthetic Scheme 1, in which n is 0, R¹-R⁴ are eachhydrogen, X is —CH₂—, and R⁵ and R⁶ are each —CH₂OH.

With reference to Synthetic Scheme 1, endo-2,3-norbornene dicarboxylicacid anhydride (also referred to as endo-nadic anhydride) (1a) isexposed to a temperature of 140 to 210° C. for a sufficient period oftime, such as from 15 minutes after melting to 24 hours, followed byrepeated recrystallizations, such as 2 or more recrystallizations fromethyl acetate or toluene, so as to form exo-2,3-norbornene dicarboxylicacid anhydride (also referred to as exo-nadic anhydride) (1b).Hydrogenation of cis-exo-nadic anhydride (1b) in the presence ofhydrogen gas (H₂), palladium catalyst supported on porous carbon (Pd/C),and ethyl acetate (EtOAc), results in formation of exo-2,3-norbornanedicarboxylic acid anhydride (1c). Reduction of exo-2,3-norbornanedicarboxylic acid anhydride (1c) in the presence of lithium aluminumhydride (LiAlH₄) and ethyl ether (Et₂O) results in formation ofcis-exo-2,3-norbornanedimethanol (A2).

For purposes of further non-limiting illustration, the polycycliccis-endo 2,3-diol monomer represented by Formula B can be prepared inaccordance with the following Synthetic Scheme 2, in which n is 0, R¹-R⁴are each hydrogen, X is —CH₂—, and R⁵ and R⁶ are each —CH₂OH.

With reference to Synthetic Scheme 2, cis-endo-2,3-norbornenedicarboxylic acid anhydride (also referred to as endo-nadic anhydride)(1a) is hydrogenated in the presence of hydrogen gas (H₂), palladiumcatalyst supported on porous carbon (Pd/C), and ethyl acetate (EtOAc),results in formation of endo-2,3-norbornane dicarboxylic acid anhydride(2a). Reduction of endo-2,3-norbornane dicarboxylic acid anhydride (2a)in the presence of lithium aluminum hydride (LiAlH₄) and ethyl ether(Et₂O) results in formation of cis-endo-2,3-norbornanedimethanol (B2).

The polycyclic endo-exo-2,3-diol monomer represented by Formula C can beprepared in accordance with the following Synthetic Scheme 3, which isprovided for purposes of non-limiting illustration, in which n is 0,R¹-R⁴ are each hydrogen, X is —CH₂—, and R⁵ and R⁶ are each —CH₂OH.

With reference to Synthetic Scheme 3, cyclopentadiene (3a) and diethylfumarate (3b) are reacted together by means of Diels-Alder reaction atreduced temperature, such as 0° C., so as to formendo-exo-2,3-norbornene bis(ethylcarboxylate) (3c). Hydrogenation ofendo-exo-2,3-norbornene bis(ethylcarboxylate) (3c) in the presence ofhydrogen gas (H₂), palladium catalyst on porous carbon (Pd/C), and ethylacetate (EtOAc), results in formation of endo-exo-2,3-norbornanebis(ethylcarboxylate) (3d). Reduction of endo-exo-2,3-norbornanebis(ethylcarboxylate) (3d) in the presence of lithium aluminum hydride(LiAlH₄) and ethyl ether (Et₂O) results in formation ofexo-endo-2,3-norbornanedimethanol (C2).

The polycyclic cis-exo-2,3-diol monomer represented by Formula A can beprepared in accordance with the following Synthetic Scheme 4, which isprovided for purposes of non-limiting illustration, in which n is 0,R¹-R⁴ are each hydrogen, X is —CH₂—, R⁵ is —OH and R⁶ is —CH₂OH.

With reference to Synthetic Scheme 4,hexahydro-4H-5,8-methanobenzo[d]-exo-[1,3]dioxane (4a) is converted tocis-exo-(3-acetoxynorborn-2-yl)methyl acetate (4b) andcis-exo-((3-acetoxynorborn-2-yl)methoxy)methyl acetate (4c) in thepresence of acetic anhydride (Ac₂O) and a catalytic amount of sulfuricacid (H₂SO₄). The intermediates (4b) and (4c) are converted tocis-exo-3-(hydroxymethyl)norbornan-2-yl (A3) in the presence of waterand a catalytic amount of sodium hydroxide (NaOH).

The polycyclic cis-endo-2,3-diol monomer represented by Formula B can beprepared in accordance with the following Synthetic Scheme 5, which isprovided for purposes of non-limiting illustration, in which n is 0,R¹-R⁴ are each hydrogen, X is —CH₂—, R⁵ is —OH and R⁶ is —CH₂OH.

With reference to Synthetic Scheme 5,hexahydro-4H-5,8-methanobenzo[d]-endo-[1,3]dioxane (5a) is converted tocis-endo-(3-acetoxynorborn-2-yl)methyl acetate (5b) andcis-endo-((3-acetoxynorborn-2-yl)methoxy)methyl acetate (5c) in thepresence of acetic anhydride (Ac₂O) and a catalytic amount of sulfuricacid (H₂SO₄). The intermediates (5b) and (5c) are converted tocis-endo-3-(hydroxymethyl)norbornan-2-yl (B3) in the presence of waterand a catalytic amount of sodium hydroxide (NaOH).

The optional polycyclic diols represented by Formulae D, E, F and G canbe prepared by art-recognized methods. For purposes of non-limitingillustration, the optional polycyclic diol represented by Formula F canbe synthesized in accordance with the following Synthetic Scheme 6,where m is 0, R⁷-R¹⁰ are each hydrogen, Z is —CH₂—, R¹¹ is —OH and R¹²is —CH₂OH.

With reference to Synthetic Scheme 6, 2,3-norbornene (6a) is convertedto (2-(formyloxy)norborn-7-yl)-exo-methyl formate (6b) in the presenceof formic acid (HCOOH) sulfuric acid (H₂SO₄) and formaldehyde (H₂CO).Intermediate (6b) is then converted to7-(hydroxymethyl)norbornan-2-exo-ol (F1) in the presence of sodiumhydroxide (NaOH) and methanol (MeOH).

The polycarbonate polymer embodiments according to the present inventioncan be prepared by art-recognized methods that include, but are notlimited to the methods of Polymerization Examples 1-12 and can beselected from homopolymers, such as homopolymers containing a singletype of repeating unit derived from any one of Formulae A through Gand/or I through XV or random copolymers, or block copolymers, oralternating copolymers, which are alternatively referred to herein asrandom polymers, block polymers and alternating polymers. The random,block and alternating polycarbonate copolymer embodiments according tothe present invention can include two or more types of repeating unitsderived from at least one of Formulae A through G and optionally atleast one of Formulae I through XV.

Some of the polycarbonate polymer embodiments as described above canencompass repeating units derived from polycyclic 2,3-diols selectedfrom each of Formulae A through G or selected from any one or two ofsuch formulae.

When such a polycarbonate polymer embodiments encompass repeating unitsderived from two polycyclic 2,3-diol monomers represented by andselected from, for example, Formula A, Formula B and Formula C, the molepercent ratio of such repeating units can be from 1 to 99, from 10 to90, from 30 to 70, or any other subratio subsumed in any of such recitedratios, provided that the sum of mole percents of such repeating unitsis 100 mole percent.

Some of the polycarbonate polymer embodiments of the present inventionencompass monomers represented by and selected from each of, forexample, Formula A, Formula B and Formula C. Such embodiments will beunderstood to include mole percent ratios where any single mole percentis 1, any single mole percent is 98 as well as any other subratiosubsumed therein. Without limitation, such mole percent ratios include,1 to 1 to 98, 10 to 10 to 80, and 33.33 to 33.33 to 33.33, provided thatthe sum of mole percents of such repeating units is 100 mole percent.

For some polycarbonate polymer embodiments in accordance with thepresent invention, R⁵ and R⁶ of each of Formulae A through G, can beindependently selected from —(CH₂)_(p)—OH, where p is 0, 1, 2 or 3.While for other such embodiments, for at least one of R⁵ and R⁶, p isindependently 1, 2 or 3, for example providing —CH₂OH where p is 1. Instill other such embodiments, for each of R⁵ and R⁶, p is independently1, 2 or 3.

In the Examples provided hereinbelow general procedures for theformulating polymer composition embodiments in accordance with thepresent inventions are provided. Such polymer composition embodiments,alternately referred to herein as TFU polymer compositions, encompass apolymer embodiment, a carrier solvent, and a fluxing agent, for example,formic acid (FA). While it should be understood that each of the TFUpolymer compositions mentioned were actually made and results of theseveral evaluations made reported, the inventors believe that providingsuch general procedures is sufficient to demonstrate that embodiments inaccordance with the present invention have been actually reduced topractice and will be useful for providing both holding ofmicroelectronic components during and post their assembly ontosubstrates as well as sufficient fluxing activity to provide excellentsolder bonds.

As used herein, a “fluxing agent” will be understood to mean a chemicalcleaning agent that facilitates soldering by removing oxidation from themetals to be joined. Fluxing agents may include, but are not limited toacidic, neutral, or basic compositions. Exemplary embodiments of fluxingagents include, but are not limited to, formaldehyde, formic acid,2-nitrobenzoic acid, malonic acid, citric acid, malic acid and succinicacid. Other exemplary fluxing agents include oxalic acid, adipic acid,glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,maleic acid, tartaric acid, lactic acid, mandelaic acid, glyceric acid,valeric acid, caproic acid, phenylacetic acid, benzoic acid, salicylicacid and aminobenzoic acid. For ease of comparison and understanding,formic acid (FA) was used as the fluxing agent in the examples thatfollow, such examples demonstrating that FA provides excellent fluxingby and through the solder reflow data presented. Additionally, storagestability data is provided to demonstrate that storage of polymerformulation embodiments of the present invention at elevatedtemperatures does not indicate any apparent M_(w) change in the polymerof such embodiments in the presence of FA or other commonly employedfluxing agents (See, Tables 5 and 6, below).

As used herein, a “carrier solvent” will be understood to mean a solventused to form a solution of a selected polymer embodiment in accordancewith the present invention and a selected fluxing agent thus forming apolymer composition embodiment in accordance with the present invention.It will further be understood that such a carrier solvent will beessentially unreactive with the selected polymer embodiment as well asthe selected fluxing agent. That is to say that such polymer compositionembodiment will exhibit desirable storage stability as well as providingdesirable tacking, fluxing and underfill. Exemplary carrier solventsinclude, but are not limited to, cyclohexanone, cyclopentanone,diethylene glycol dimethyl ether, gamma-butyrolactone (GBL),N,N-dimethylacetamide, N,N-dimethylformamide, anisole, acetone, methyl3-methoxypropionate, tetrahydrofuran (THF) and mixtures thereof.

Further, while the solder reflow data presented hereinbelow was obtainedusing tin-copper eutectic solder balls (Sn99.3Cu0.7), other types ofsolders, and in particular lead free solders, such as SAC305(Sn96.5Ag5Cu0.5 from M.G. Chemical) or K100 and K100LD (Sn99.4Cu0.6 andSn99.5Cu0.5, respectively, Kester, Inc.), can also be used effectivelywith or without adjusting any particular formulation. Still further, itwill be understood that the inventors demonstrate through the examplesprovided hereinbelow that there is no single effective TFU polymercomposition, but rather many formulations of a polymer embodiment, acarrier solvent, and a fluxing agent that can be made available for awide range of microelectronic component assembly. That is to say,polymer composition embodiments in accordance with the present inventioncan be readily tailored with regard to decomposition temperature,tackiness, M_(w), and fluxing activity to provide excellent solutionsfor a wide range of assembly processing.

In summary, polymer composition embodiments of the present inventionhaving formic acid (FA) as the fluxing agent were prepared and evaluatedto demonstrate the extent of their fluxing activity. Referring to Table3, it can be observed that Examples C1-C3, demonstrate solder spread orreflow, i.e., the diameter of the spread solder was about 1.6 times thediameter of the original solder ball as represented in the controlsample, C4. While FA was the only fluxing agent used for theaforementioned reflow examples, it will be understood that other knownfluxing agents, such as are mentioned above, are also within the scopeof the TFU polymer composition embodiments of the present invention.Further, while Solder Flux Examples C1-C3 employ syringe application ofthe formulations of Examples B1-B3, any other appropriate method forapplying the formulations can be used. Thus, in addition to syringeapplication, exemplary application methods include, among others, spincoating, spraying, dip-coating and doctor blading.

In the Examples and Tables presented below, several trade names and orabbreviations are used to identify components of the polymer compositionembodiments of the present invention. While in most cases such examplesalso provide the full name of such components, chemical names for somecomponents may not be completely identified in the Examples.

EXAMPLES A. Polymer Synthesis Polymerization Example 1cis-exo-2,3-Norbornanedimethanol and cis-endo-2,3-Norbornanedimethanol

To an appropriately sized and equipped multi-necked reaction vessel,were added 22.5 grams of cis-exo-2,3-norbornanedimethanol (144 mmol),15.0 grams of cis-endo-2,3-norbornanedimethanol (96 mmol), 51.3 grams ofdiphenyl carbonate (240 mmol), and 12 milligrams of lithium hydride (1.5mmol). The contents of the vessel were heated to and held at 120° C.under a nitrogen sweep for a period of time sufficient to form areaction solution and then held at that temperature for 2 hours, undernitrogen, with constant stirring. The pressure of the reaction vesselwas then reduced, isothermally, to 10 kPa and stirring continued for anadditional hour. Then the pressure of the vessel was further reduced,isothermally, to 0.5 kPa, and stirred for an additional 1.5 hours,followed by increasing the temperature of the reaction solution to 180°C. and maintaining that temperature, with stirring for another 1.5hours. The contents of the reaction vessel were then cooled to roomtemperature, tetrahydrofuran (800 mL) added with stirring and theresulting solution filtered. The filtrate was then added dropwise to 8liters of a 9:1 methanol:water solution causing precipitation of thedesired polymer. After isolating the precipitate and washing it with anadditional 4 liters of a 9:1 methanol:water solution, the polymer wasdried to constant weight. 30.7 grams of polymer were obtained. Thepolymer yield was 70%, its molecular weight (M_(w)), was 41,000 andpolydispersity index (PDI) was 1.70.

Polymerization Example 2 1,3-Cyclohexanediol andcis-exo-2,3-Norbornanedimethanol

The procedure used in Example 1 was followed except that the reactionvessel was charged with 20.5 grams of 1,3-cyclohexanediol (176 mmoles(TCI America, Portland, Oreg.)); 15.5 grams ofcis-exo-2,3-norbornanedimethanol (99 mmoles); 56.6 grams of diphenylcarbonate (264 mmoles); and 13.2 mg of lithium hydride (1.7 mmoles).28.1 grams of polymer was obtained in a yield of 69%. The polymer wasfound to have a M_(w), of 47,000, and a PDI of 1.75.

Polymerization Example 3 1,3-Cyclohexanediol andcis-endo-2,3-Norbornanedimethanol

The procedure used in Example 1 was followed except that the reactionvessel was charged with 19.2 grams of 1,3-cyclohexanediol (165 mmoles,TCI America); 14.5 grams of cis-endo-2,3-norbornanedimethanol (93 mmol);53 grams of diphenyl carbonate (248 mmol); and 10.1 mg of lithiumhydride (1.3 mmol). 28.7 grams of polymer were obtained in a yield of 76percent. The polymer M_(w) was 38 k, with a PDI of 1.61.

The properties of the polycarbonates obtained from PolymerizationExamples 1-3 are summarized below in Tables 1 and 2. In Table 2, thecolumn “End Ph” is the chain-end phenyl group percent mole valuesindicating the theoretical amount of phenol, based on the initial amountof diphenyl carbonate raw material charged and not removed duringpolymerization; the column “Mole %” provides values determined by NMRanalysis, and indicate the percent of monomer units in the polymersderived from cis-exo- or cis-endo-2,3-norbornanedimethanol monomer, asindicated; and the column “Solubility” is a qualitative representationas to whether a target resin content (RC, 20 wt %) of the polymer wassoluble or insoluble in the indicated solvent, where “A” refers toanisole and “G” refers to gamma-butyrolactone.

TABLE 1 % Ex. # Yld M_(w) PDI T_(g) ° C. T_(d5) ° C. T_(d50) ° C.T_(d95) ° C. PE1 70 41,000 1.70 89 279 291 298 PE2 68 47,000 1.75 112262 285 309 PE3 74 38,000 1.61 117 269 293 315

TABLE 2 Example End Ph (a) Mole % (b) Solubility (c) # (%) (Empirical)RC = 20% PE1 10 exo = 59 A: soluble G: insoluble PE2 18 exo = 41 A:soluble G: soluble PE3 17 endo = 41 A: soluble G: soluble

Polymerization Example 4 cis-exo-2,3-Norbornanedimethanol homopolymer

The procedure used in Example 1 was followed except that the reactionvessel was charged with 25.0 g (160 mmol) of cis-exo-2,3-norbornanedimethanol and 34.3 g (185 mmol) of diphenyl carbonate and 6.4 mg (0.80mmol) of lithium hydride. After initial polymer precipitation, thematerial was redissolved in tetrahydrofuran and precipitated once moreinto pure methanol. After filtration and drying in a dynamic vacuumoven, 23.5 g white polymer was obtained. Polymer properties aresummarized as follow: M_(w)=72 k, PDI=3.0, T_(g)=85° C., T_(d50)=313° C.

Polymerization Example 5 5-exo-Phenyl-cis-endo-2,3-Norbornanedimethanolhomopolymer

The procedure used in Example 1 was followed except that the reactionvessel was charged with 25.0 g (108 mmol) of5-exo-phenyl-cis-endo-2,3-norbornanedimethanol and 23.1 g (108 mmol) ofdiphenyl carbonate and 58.0 mg (0.55 mmol) of sodium carbonate. Polymersolution in tetrahydrofuran was dropwise added to pure methanol duringprecipitation. After filtration and drying in a dynamic vacuum oven,19.6 g white polymer was obtained. Polymer properties are summarized asfollow: M_(w)=63 k, PDI=2.0, T_(g)=114° C., T_(d50)=321° C.

Polymerization Example 6 5-exo-Phenyl-cis-exo-2,3-Norbornanedimethanolhomopolymer

The procedure used in Example 1 was followed except that the reactionvessel was charged with 10.0 g (43 mmol) of5-exo-phenyl-cis-exo-2,3-norbornanedimethanol and 9.2 g (43 mmol) ofdiphenyl carbonate and 1.7 mg (0.22 mmol) of lithium hydride. Polymersolution in a mixture of methylene chloride and tetrahydrofuran wasdropwise added to pure methanol during precipitation. After filtrationand drying in a dynamic vacuum oven, 9.1 g white polymer was obtained.Polymer properties are summarized as follow: M_(w)=49 k, PDI=2.0,T_(g)=115° C., T_(d50)=284° C.

Polymerization Example 7 trans-2,3-Norbornanedimethanol homopolymer

The procedure used in Example 1 was followed except that the reactionvessel was charged with 70.0 g (448 mmol) of trans-2,3-norbornanedimethanol and 96.5 g (450 mmol) of diphenyl carbonate and 238 mg (2.24mmol) of sodium carbonate. Polymer solution in tetrahydrofuran wasdropwise added to pure methanol during precipitation. After filtrationand drying in a dynamic vacuum oven, 75.4 g white polymer was obtained.Polymer properties are summarized as follow: M_(w)=177 k, PDI=2.1,T_(g)=81° C., T_(d50)=360° C.

Polymerization Example 8 Isosorbide Homopolymer

The procedure used in Example 1 was followed except that the reactionvessel was charged with 102.3 g of isosorbide (0.7 mol, Cargill Inc.,Minneapolis, Minn.); 149.95 g of diphenyl carbonate (0.7 mol); and 3.0mg of cesium carbonate (0.01 mmol). The crude polymer was dissolved ingamma-butyrolactone (GBL). About 119 g of the poly(isosorbide)homopolymer was obtained after precipitation into 7:3 isopropanol:water,filtration, and vacuum drying. Polymer properties are summarized asfollow: M_(w)=38.5 k, PDI=2.61, T_(g)=167° C., T_(d50)=376° C.

Polymerization Example 9 Isosorbide and trans-2,3-Norbornanedimethanol

The following were added to a 250 mL round flask charged with a suitablysized magnetic stirrer: 13.17 g of isosorbide (90 mmol, Cargill Inc.),14.09 g of trans-2,3-norbornanedimethanol (90 mmol), 38.63 g of diphenylcarbonate (180 mmol), and 95.6 mg of sodium carbonate (9.0 mmol). Theflask was evacuated to 1.3 kPa and refilled with nitrogen three times.The contents were kept under nitrogen when the flask was immersed intoan oil bath at 120° C. The reaction was kept at 120° C. for 2 hoursunder a nitrogen sweep. The contents of the flask were then subjected toa reduced pressure of 10 kPa at 120° C. for 1 hour. Subsequently, theoil bath temperature was gradually increased from 120 to 180° C. at 10kPa, during which a majority of phenol is distilled over and collectedin a liquid nitrogen cooled trap. The pressure was gradually reduced to0.7 kPa and the reaction was held at 180° C. for an additional 2 hours.The contents of the flask were cooled to room temperature and dissolvedin a suitable amount of tetrahydrofuran, such as 150 mL, with orbitshaking. The solution was further diluted to 500 mL with tetrahydrofuranand filtered. The filtered solution was dropwise added to 5 liters ofmethanol. The white polymer was collected by filtration and dried in avacuum oven (70° C., 29.4 inches water vacuum) for 18 hours. Dry polymerweight was 30.2 g. Polymer properties are summarized as follow: M_(w)=32k, PDI=1.94, T_(g)=116° C., T_(d50)=372° C.

Polymerization Example 10 Isosorbide and 1,4-Cyclohexanedimethanol

The procedure used in Example 10 was followed except that the reactionvessel was charged with 29.04 g of isosorbide (199 mmol, Cargill Inc.),28.7 g of 1,4-cyclohexanedimethanol (199 mmol), 85.2 g of diphenylcarbonate (398 mmol), and 211 mg of sodium carbonate (19.9 mmol). Drypolymer weight was 65.1 g. Polymer properties are summarized as follow:M_(w)=72 k, PDI=2.84, T_(g)=110° C., T_(d50)=373° C.

Polymerization Example 11 Cyclic Norbornane Spirocarbonate Homopolymer

sec-Butyllithium (0.21 mL, 1.4 M in cyclohexanone) was added tospiro[bi-cyclo[2.2.1]heptane-2,5′-[1,3]dioxan]-2′-one (15 g, 82.3 mmol)in toluene (200 mL) at 0° C. under a nitrogen blanket. The reactionmixture was stirred at 0° C. for 5 hours and then gradually allowed towarm to room temperature. Stirring was continued for an additional 12hours at room temperature after which the polymer was precipitated frommethanol, and dried under vacuum to give 9 g of a white polymer. PolymerM_(w) was determined to be 32 k with a PDI of 1.63 and a T_(d50)=284° C.

B. Fluxing Formulation Examples Example B1 Formulation of Polycarbonatefrom 1,3-Cyclohexanediol and endo-endo-2,3-Norbornanedimethanol withFormic Acid in GBL

Dry polymer (4.54 g) prepared following procedures in Polymer Example 3was added to gamma-butyrolactone (GBL) to give a polymer solution with atotal weight of 12.8 g (35.3 wt % resin content). A clear, viscous,homogeneous polymer solution was obtained by roller mixing for a minimumof 12 hours. The viscous solution was filtered by passing through 1.0 μmdisc filters made of PTFE, and the viscosity was determined to be 17500cPs at 25° C. with a Brookfield viscometer (Model DV I Prime). Formicacid (0.67 g, 5 wt % of total solution) is then added and a homogeneousformulation is obtained after roller mixing for 8 hours.

Example B2 Formulation of Polycarbonate from Isosorbide andendo-exo-2,3-Norbornanedimethanol with Formic Acid in GBL

A polycarbonate formulation according to embodiments of the presentinvention was prepared in accordance with the procedure described inExample B1 with 5.25 g dry polymer from Polymer Example 9 to give a basepolymer solution of 15.0 g (35.0 wt % resin content). The viscosity wasdetermined to be 4600 cPs. Formic acid added is 0.78 g.

Example B3 Formulation of Polycarbonate from Isosorbide and1,4-Cyclohexanedimethanol with Formic Acid in GBL

A polycarbonate formulation according to embodiments of the presentinvention was prepared in accordance with the procedure described inExample B1 with 2.00 g dry polymer from Polymer Example 10 to give abase polymer solution of 10.0 g (20.0 wt % resin content). The viscositywas determined to be 8000 cPs. Formic acid added is 0.52 g.

C. Solder Flux Evaluation with Formic Acid in GBL

The formulations of Examples B1-B3 were used to provide the data forEvaluations C1-C3, respectively, as shown in Table 3. The process usedfor these examples was as follows: the formulation was dispensed asdistinct spots with a 27-gauge needle onto a copper plate (1.7 cm×3.4cm) with a partly oxidized surface. A solder ball (Sn99.3Cu0.7; 600 μm)was carefully transferred to the top of each of the spots on the copperplate. The entire plate, mounted onto a device, was subjected to thermalreflow by increasing the ambient temperature surrounding the plate fromroom temperature to between 230 and 260° C. in less than 2 minutes asthe plate was passing through a reflow oven. The final temperature wasthen maintained for an additional 2 minutes before allowing the plate toreturn to room temperature. It was observed during the transfer of theplate carrying the carefully placed solder balls, that each spot ofpolymer composition held the solder ball placed thereon in position,thus demonstrating that such composition was a useful tacking agent. Thediameter of the solder material as measured after reflow, ranged from930 to 990 μm which when compared to the control (C4) demonstratedexcellent fluxing. The formulation for the control (C4) was formulationB2 without formic acid. The results of the solder reflow of ExamplesC1-C4 are shown in Table 3, below.

TABLE 3 Formulation Loading of Solder diameter from Formic Acid afterreflow Example Example (wt %) (μm) C1 B1 5 930 C2 B2 5 990 C3 B3 5 940C4 Control 0 600

D. Thermal Stability Examples

D1: Isothermal Thermogravimetric Analysis of Polycarbonate fromIsosorbide and endo-exo-2,3-Norbornanedimethanol

A polymer composition was formulated from a polymer made in the mannerof Polymer Example 9 (M_(w)=32 k) and an appropriate amount ofgamma-butyrolactone. The composition was spin-coated onto a four-inchsilicon substrate and baked at 120° C. for 10 minutes to yield a clearfilm. A sample of the film was peeled from the substrate and analyzed byisothermal thermogravimetric analysis at 220° C. The weight loss, afterone hour was less than 2% compared to initial film weight. The weightloss of a similar sample at 260° C. was less than 5% in one hour,suggesting that the material had thermal stability within the 200° C. to260° C. window.

D2: Film Thickness Evaluation Upon Thermal Reflow

A polymer composition was formulated from a polymer made in the mannerof Polymer Example 9 (M_(w)=32 k) and an appropriate amount ofgamma-butyrolactone. The composition was spin-coated onto a four-inchsilicon substrate and baked at 120° C. for 10 minutes to give anapproximately 2 μm thick film. The silicon substrate was heated in areflow oven by increasing the temperature surrounding the plate fromroom temperature to between 230° C. and 260° C. in less than 2 minutes.The substrate was held at that temperature for an additional 2 minutesand then allowed to cool to room temperature. The final film thicknesswas recorded and compared to the initial film thickness prior toheating. As shown in Table 4, the thickness variation is ≦1%, wellwithin typical film thickness measurement error, and no deterioration offilm quality was observed. All data indicate that the material issuitable for use as a permanent material between 230° C. and 260° C.

TABLE 4 Film Thickness Data Initial Film Post-reflow % Thickness filmthickness Change in Polycarbonate (μm) (μm) Thickness PE9 2.07 2.05 1.0PE9 1.78 1.77 0.6

E. Storage Stability Examples of Formulations with Formic Acid

For the following examples, the formulations with formic acid (FA) ingamma-butyrolactone were prepared and stored at 65° C. for one week,after which the final molecular weight M_(w)(Final) was determined. TheM_(w) ratio in Table 5 was determined by evaluating the ratio ofM_(w)(final)/M_(w)(initial), where M_(w)(initial) was taken as themolecular weight determined prior to heating to 65° C. As shown, eachsample indicated stability for the time it was stored.

TABLE 5 M_(w) Loading of M_(w) Formulation (Initial) FA (wt %) Ratio B152k 5.0 0.99 B1 52k 10.0 0.97 B2 31k 5.0 0.99 B2 31k 10.0 0.97

F. Storage Stability Examples of Formulations with Other Acidic FluxingAgents

For each of the previously known acidic fluxing agents listed in Table6, below, a formulation of poly(propylene carbonate) (Novomer, Inc.) ingamma-butyrolactone was prepared using the indicated loading of FluxingAgent. An initial M_(w) was determined and the sample stored at 95° C.for 48 hours, after which a final M_(w) was determined and the ratio ofM_(w)(final)/M_(w)(initial) calculated. While the storage time for theseformulations was shorter than for the storage stability examples of theformic acid formulations reported in Table 5, it is believed that withthe higher temperature at which these formulations were stored, theconditions for these storage stability examples were at least asstringent as were the conditions for the formic acid storage stabilityexamples. Therefore, as shown, for each of formulations shown in Table6, indicated stability.

TABLE 6 Loading Initial M_(w) Fluxing agent (wt %) M_(w) Ratio2-Nitrobenzoic 5.0 72K 0.99 acid Malonic acid 3.0 72K 0.97 5.0 72K 0.97Citric acid 2.0 71K 0.98 5.0 72K 0.94 Malic acid 5.0 73K 0.95 Succinicacid 3.0 72K 0.97 5.0 73K 0.95

By now it should be realized that TFU polymer composition embodiments inaccordance with the present invention have been provided herein thatdemonstrate both the ability to provide fluxing for solder reflow typeof attachment of microelectronic components to a substrate, and theability to act as an underfill connection to hold such components inplace prior to, during, and after the solder reflow process.Additionally it should be realized that such TFU compositions canencompass a variety of polymer embodiments where such polymerembodiments can be tailored to have a desired T_(d50) by and throughadjusting the M_(w) of such polymers and/or the composition of suchpolymer. Further, it should be realized that any one or more of thepreviously mentioned fluxing agents in combination with any one or moreof the aforementioned polymer embodiments and any one or more of theaforementioned carrier solvents to form a desired TFU polymercomposition in accordance with the present invention. Further, it shouldbe realized that while the formulation examples above demonstratepolymer weight percents from 20 to more than 35, some TFU polymercomposition embodiments encompass ranges of polymer weight percentagesfrom 15 to 50 and still others from 10 to 80; where such various wt % ofpolymer are effective to select a desired viscosity of the TFUcomposition as well as properties of the resulting underfill formedtherefrom.

It should be further realized that the TFU polymer compositions of thepresent invention are useful for forming a variety of microelectronicdevice assemblies where a first substrate having a plurality of firstcontacts disposed over a first surface, for example a semiconductor diehaving electrical contact pads or through silicon via electrical contactpads disposed over a first surface, is electrically and physicallycoupled to a second substrate having a second plurality of contact padsdisposed over a second surface, the first and second plurality ofcontact pads being at least substantially aligned with one another. Theelectrical and physical coupling being accomplished by providing solderpreforms, for example solder balls, to individual contacts of one orboth of the first and second plurality of contact pads, applying a TFUpolymer composition to one or both of the first and second surfaces suchthat the TFU polymer composition encapsulates the solder preforms.Further to accomplishing the physical and electrical coupling, the firstand second substrates brought into contact with one another through thelayer of TFU polymer to form a preassembly structure which is thenheated to a temperature that effective to both allow for the solderpreforms to form electrical coupling of the first and second pluralityof contacts, but to also be effective for the TFU polymer to encapsulatethe solder preforms and physically couple the first substrate to thesecond substrate.

1. A TFU polymer composition comprising: a polymer comprising apolycarbonate having a molecular weight (M_(w)) from 5,000 to 300,000; acarrier solvent; and a fluxing agent.
 2. The polymer composition ofclaim 1 where the fluxing agent is selected from formaldehyde, formicacid, 2-nitrobenzoic acid, malonic acid, citric acid, malic acid andsuccinic acid.
 3. The polymer composition of claim 2, where the fluxingagent is formic acid.
 4. The polymer composition of claim 1 where thepolycarbonate is selected from a poly(alkylene carbonate) or a polymerformed from stereospecific norbornane diol and/or dimethanol monomers.5. The polymer composition of claim 4 where the polymer formed fromstereospecific norbornane diol and/or dimethanol monomers is one of aexo-exo-2,3-polynorbornane dimethyl carbonate andendo-endo-2,3-polynorbornane dimethyl carbonate polymer, a1,3-polycyclohexyl carbonate and endo-exo-2,3-polynorbornane dimethylcarbonate polymer, a poly(isosorbyl carbonate) andtrans-2,3-polynorbornane dimethyl carbonate polymer.
 6. The polymercomposition of claim 1 where the polymer comprises repeating unitsderived from norbornane diol monomers, norbornane dimethanol monomers,and diol monomers represented by Formulae I to XV.
 7. The polymercomposition of claim 1 where the polymer is 15 to 80 wt % of the polymercomposition.
 8. The polymer composition of claim 7 where formic acidcomprises from 0.5 to 10.0 wt % of the composition based on the totalweight of the polymer.
 9. The polymer composition of claim 1 where thecarrier solvent is selected from cyclohexanone, cyclopentanone,diethylene glycol dimethyl ether, gamma-butyrolactone (GBL),N,N-dimethylacetamide, N,N-dimethylformamide, anisole, acetone, methyl3-methoxypropionate, tetrahydrofuran (THF) and mixtures thereof.
 10. Thepolymer composition of claim 9, where the carrier solvent is GBL.
 11. Amethod for forming a microelectronic component assembly comprising:providing a first substrate having first contact regions disposed over afirst surface; providing a second substrate having second contactregions disposed over a second surface; providing solder preformsdisposed over one or more of the first contact regions or one or more ofthe second contact regions; forming a layer of TFU polymer overlying andencapsulating the solder preforms; contacting the first surface of thefirst substrate to the second surface of the second substrate where thelayer of TFU polymer is disposed therebetween, the first contact regionsare aligned with the second contact regions and where a preassemblystructure is formed; and heating the preassembly structure to atemperature effective to (1) cause the solder preforms to physically andelectrically couple the one or more of the first contact regions to theone or more of the second contact regions and to (2) form a polymerunderfill physically coupled to the first and second substrates.
 12. Themethod of claims 11 where forming a layer of TFU polymer overlying andencapsulating the solder preforms comprises forming such layer overlyingan active surface of a microelectronic device having solder ballsdisposed on contact pads.